I can run a game of original D&D or Flashing Blades right now. I might or might not have to get up and consult a rulebook.

I could run a game of BECMI, AD&D 1e or 2e, Champions, Fantasy Hero, or TOON with two or three days notice.

Give me a week or two, and I could run Pendragon or 3.5e.

For a game I've never seen before, I want four to six weeks to prepare.

But Chivalry and Sorcery? At least six months, and only if I had nothing else I had to do in that time.